1. Field of the Invention
This invention relates to monomer and polymer compositions useful to form biomedical adhesives, sealants, bioactive agent release matrices, and implants. More particularly, this invention relates to biocompatible monomer and polymer compositions particularly useful for medical, surgical and other in vivo applications.
2. Related Developments
The products in primary use for wound closure are surgical sutures and staples. Sutures are recognized to provide adequate wound support. However, sutures cause additional trauma to the wound site (by reason of the need for the needle and suture to pass through tissue) and are time-consuming to place, and, at skin level, can cause unattractive wound closure marks. Surgical staples have been developed to speed wound apposition and provide improved cosmetic results. However, surgical staples also impose additional wound trauma and require the use of ancillary and often expensive devices for positioning and applying the staples.
To overcome these drawbacks, fast-acting surgical adhesives have been proposed. One group of such adhesives is the monomeric forms of alpha-cyanoacrylates.
Reference is made, for example, to U.S. Pat. Nos. 3,527,841 (Wicker et al.); 3,722,599 (Robertson et al.); 3,995,641 (Kronenthal et al.); and 3,940,362 (Overhults), which disclose that alpha-cyanoacrylates are useful as surgical adhesives. All of the foregoing references are hereby incorporated by reference herein.
Typically, when used as adhesives and sealants, cyanoacrylates are applied in monomeric form to the surfaces to be joined or sealed, where, typically, in situ anionic polymerization of the monomer occurs, giving rise to the desired adhesive bond or seal. Implants, such as rods, meshes, screws, and plates, may be formed of cyanoacrylate polymers, formed typically by radical-initiated polymerization.
However, a drawback to the in vivo biomedical use of alpha-cyanoacrylate monomers and polymers has been their potential for causing adverse tissue response. For example, methyl alpha-cyanoacrylate has been reported to cause tissue inflammation at the site of application.
The adverse tissue response to alpha-cyanoacrylates appears to be caused by the products released during in vivo biodegradation of the polymerized alpha-cyanoacrylates. It is believed that formaldehyde is the biodegradation product most responsible for the adverse tissue response and, specifically, the high concentration of formaldehyde produced during rapid polymer biodegradation. Reference is made, for example, to F. Leonard et al., Journal of Applied Polymer Science, Vol. 10, pp. 259-272 (1966); F. Leonard, Annals New York Academy of Sciences, Vol. 146, pp. 203-213 (1968); Tseng, Yin-Chao, et al., Journal of Applied Biomaterials, Vol. 1, pp. 111-119 (1990), and to Tseng, Yin-Chao, et al., Journal of Biomedical Materials Research, Vol. 24, pp. 1355-1367 (1990), which are both hereby incorporated by reference herein.
For these reasons, cyanoacrylates have not come into widespread use for biomedical purposes.
Efforts to increase the tissue compatibility of alpha-cyanoacrylates have included modifying the alkyl ester group.-For example, increasing the alkyl ester chain length to form the higher cyanoacrylate analogues, e.g., butyl-2-cyanoacrylates and octyl-2-cyanoacrylates, has been found to improve biocompatibility but the higher analogues biodegrade at slower rates than the lower alkyl cyanoacrylates.
Other examples of modified alpha-cyanoacrylates used in biomedical applications include carbalkoxyalkyl alpha-cyanoacrylates (see, for example, U.S. Pat. No. 3,995,641 to Kronenthal et al.), fluorocyanoacrylates (see, for example, U.S. Pat. No. 3,722,599 to Robertson et al.), and alkoxyalkyl 2-cyanoacrylates (see, for example, U.S. Pat. No. 3,559,652 to Banitt et al.). Other efforts have included mixing alpha-cyanoacrylates with dimethyl methylenemalonate and higher esters of 2-cyanoacrylic acid (see, for example, U.S. Pat. No. 3,591,676 to Hawkins et al.).
In other efforts to increase the usefulness of alpha-cyanoacrylate adhesive compositions for surgical applications, certain viscosity modifiers have been used in combination with alkyl alpha-cyanoacrylate monomers, such as methyl alpha-cyanoacrylate. See, for example, U.S. Pat. Nos. 3,564,078 (wherein the viscosity modifier is poly(ethyl 2-cyanoacrylate)) and 3,527,841 (wherein the viscosity modifier is poly(lactic acid)), both patents being to Wicker et al.
Techniques for suppressing formaldehyde in industrial processes utilizing synthetic polymeric resins are known. However, the concept of suppressing formaldehyde as a mechanism for improving biocompatibility of polymers that biodegrade in vivo has not been suggested.